The invention relates generally to alarm systems for fire and burglary, in particular for fire in Christmas trees.
The fire hazard associated with illuminated Christmas trees that are displayed during the Christmas season, and often left unattended while connected to the electric power line, has long been recognized. The hazard stems from the facts that the trees are usually in a very dried-out condition and therefore very vulnerable to being ignited, and once ignited, they burn with an intensity that makes quick action necessary if disaster shall be averted. Even artificial trees are subject to electrical fires.
Fire detecting and alarming apparatus has been well known and used for a long time. Early fire detectors were based on the rapid temperature rise in a room exposed to fire, as detected by suitable temperature sensors positioned near the ceiling. Fire and smoke detectors of more recent years make use of other more sensitive sensing methods. One of these methods employs the reflection of light from finely dispersed smoke particles in a light beam, as seen by a sensitive photo diode. Another method employs the detection of ionized air which develops whenever a fire occurs.